This invention relates to an image forming apparatus being divided into an upper unit and a lower unit, with the upper unit rotatably supported on the lower unit, and more particularly to a paper conveying roller for the image forming apparatus having a paper conveying passage formed on the boundary surface of the upper and lower units, with one of a pair of paper conveying rollers disposed on the upper unit and the other pair on the lower unit.
A paper conveying apparatus used in an image forming apparatus such as copying machine is composed of a pair of paper conveying rollers, conveying guide, and others. The paper conveying passage including these paper conveying rollers and conveying guide is disposed from the paper feed part to the paper discharge part of the image forming apparatus, and it is designed to process image forming on the paper in the process of conveyance. In a copying machine, for example, a photosensitive drum is disposed within the paper conveying passage, and the paper being conveyed is caused to contact with the surface of the photosensitive drum in the transfer process during the copying process, and the electrostatic toner image formed on the photoreceptor surface is transferred to the paper. In this composed copying machine, in order to transfer the toner image formed on the surface of photosensitive drum onto a correct position of the paper, the conveyance of paper must be synchronized accurately with the rotation of the photosensitive drum, and the capability of the paper conveying passage must be improved, too.
On the other hand, for the ease of removal of a jamming paper, in existing commercial products, for example, the image forming apparatus is divided into upper and lower units, and the upper unit is rotatably pivoted on the lower unit, while a paper conveying passage is formed on the boundary surface of the upper and lower units. In such an image forming apparatus, one of a pair of paper conveying rollers in the paper conveying passage is disposed on the upper unit and the other pair is disposed on the lower unit. In the conventional image forming apparatus having such a construction, since the mounting positions of the shafts of the upper and lower rollers of the paper conveying rollers are completely fixed on the upper unit and lower unit, the relative positions of these rollers and the roller contacting pressures are not constant depending on the opening or closing state of the upper and lower units, and the capacity of the paper conveying passage is not stable. As a result, jamming occurs often or the transfer position of the electrostatic toner image is not constant.